A case of exaggerated exuberance: Iatrogenic atrioventricular block/intra‐Hisian Wenckebach during conduction system pacing

Isolated sinus node dysfunction with its pursuant long‐term risk for atrioventricular (AV) conduction disease poses a unique dilemma for proponents of CSP due to paucity of imprimatur guidelines. In such scenarios, the risk and prognosis of iatrogenic AV block is not well elucidated but is a valid concern. We report a case where CSP was complicated by iatrogenic AV block and peculiarly the rare phenomenon of intra‐Hisian Wenckebach.

ological cardiac resynchronization.In many centers including ours, it is exuberantly utilized as the de facto pacing strategy.Isolated sinus node dysfunction with its pursuant long-term risk for atrioventricular (AV) conduction disease poses a unique dilemma for proponents of CSP due to paucity of imprimatur guidelines.In such scenarios, the risk and prognosis of iatrogenic AV block is not well elucidated but is a valid concern.We report such a case where CSP was complicated by iatrogenic AV block and peculiarly the rare phenomenon of intra-Hisian Wenckebach.
A 74-year-old gentleman with a structurally normal heart, normal atrioventricular (AV) conduction, and narrow QRS was diagnosed with symptomatic sinus node dysfunction.
His symptoms correlated with sinus pauses noted during ambulatory electrocardiogram (ECG) monitoring.Conduction system pacing (CSP) was planned as per our default institutional protocol.Dual chamber transvenous permanent pacemaker implantation was then performed targeting the proximal left bundle branch area (LBBa).A lumenless ventricular lead (Medtronic) guided by a fixed dual curve delivery sheath (C315His, Medtronic Inc.) was utilized for this purpose.
The delivery sheath housing the retracted lead was maneuvered over the right ventricular (RV) endocardial aspect of the proximal AV septum as a prelude to target the proximal LBBa (Video S1 and Figure 1A).Coincident to this, inadvertent injury to the AV conduction system was noted (Figure 1A).There was a transient right bundle branch block (RBBB) followed by a complete AV block (CAVB).The latter was associated with a bradycardic narrow QRS junctional escape rhythm (30-35 bpm).Subsequently, backup temporary RV pacing was initiated.
The permanent pacing lead was then deployed through the sheath and screwed in after adjudicating the appropriate target site based on previously established criteria. 1By this time, there was resolution of CAVB albeit with residual first-degree AV block/RBBB and intermittent AV Wenckebach.During AV conduction, the unipolar tip electrograms obtained from the pacing lead demonstrated an LB potential (Figure 1B).LBBa capture was ascertained during pacing as demonstrated by, (i) an incomplete RBBB pattern (Qr in V1), (ii) QRS duration of 100 ms, and (iii) fixed left ventricular activation time (LVAT) of 75 ms (Figure 1B). 1 A quadripolar catheter was then placed over the His bundle area to analyze the characteristics/level of AV block.During sinus rhythm (cycle length or CL of 785 ms), there was 1:1 AV conduction with RBBB along with a split His bundle potential (H1-H2 interval of 50 ms; Figure 1C).The distal His to V (H2-V) was normal (40 ms).
Intra-Hisian Wenckebach was demonstrated during pacing at a faster CL of 520 ms (Figure 2).There is a progressive prolongation of the H1-H2 interval culminating with an intra-Hisian block (H1-but no H2).Because of this, the patient required the pacemaker to be programmed to a DDDR mode (Lower rate limit of 70 bpm, Upper rate limit of 130 bpm) with a nominal AV delay.The postimplant 12-lead ECG showed optimal evidence of CSP (Figure 3).At the time of discharge (3 days postimplant), there was 1:1 AV conduction during atrial pacing up to 130 bpm, although with residual first-degree AV block/RBBB.However, follow-up interrogation at 1 month in AAI mode revealed sinus rhythm with 1:1 AV conduction, normal PR interval (140 ms), and a narrow QRS with resolution of RBBB (Figure S2).
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.© 2023 The Authors.Journal of Arrhythmia published by John Wiley & Sons Australia, Ltd on behalf of Japanese Heart Rhythm Society.

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I G U R E 1 (A) 12-lead electrocardiogram (ECG) while maneuvering the delivery catheter toward the proximal atrioventricular (AV) septum for left bundle branch area pacing (see text for details).(B) 12-lead ECG with intracardiac EGMs from the lead tip in unipolar configuration during intrinsic rhythm and pacing at the corresponding site after lead deployment.Note the local potential labeled as a left bundle (LB) potential.The paced QRS morphology shows an incomplete right bundle branch block (RBBB) pattern with Qr in V1, QRSd of 110 ms, and left ventricular activation time (LVAT) of 75 ms.(C) 12-lead ECG with intracardiac EGMs from a quadripolar catheter placed at the His bundle region.Note the prolonged PR interval, split His potentials, and normal H2-V interval (see text for details).

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I G U R E 2 12-lead ECG with intracardiac EGMs during atrial pacing at a cycle length of 520 ms.Note the presence of 3:2 AV Wenckebach with block at intra-Hisian level (see text for details).F I G U R E 3 12-lead ECG in DDDR mode on postimplant day 1.